Deciphering the electrochemical kinetics of sulfur vacancy-assisted nitrogen-doped NiCo2S4 combined with sulfur-doped g-C3N4 towards supercapacitor applications†

In this work, an ion exchange-mediated sulfidation technique was adopted for the fabrication of a sulfur vacancy-assisted N-NiCo₂S₄/S-g-C₃N₄ nanocomposite (abbreviated as S′N-NCS/S-g-CN). The synergistic integration of S′N-NCS and S-g-CN, its impact on electrochemical capacitive performance and the charge storage mechanism of the nanocomposite were investigated via the power law as well as the Dunn and Trasatti methods. The S′N-NCS/S-g-CN nanocomposite offers the characteristic features of a battery-type electrode material. It delivers a specific capacity of 1034 C g⁻¹ at 1 A g⁻¹ in 2 M aqueous KOH electrolyte, and its performance significantly improved relative to pristine materials. Furthermore, it demonstrates excellent long-term cyclic stability performances and 94.1% capacitive retention after 10 000 cycles. A completely altered charge storage mechanism was observed from the diffusion-controlled (S′N-NCS) to capacitive-controlled mechanism in the S′N-NCS/S-g-CN electrode. Furthermore, the presence of sulfur vacancies and incorporated g-C₃N₄ in the S′N-NCS/S-g-CN nanocomposite induces a higher diffusion coefficient value of 2.38 × 10⁻⁷ cm² s⁻¹ relative to S′N-NCS (i.e., 2.21 × 10⁻⁷ cm² s⁻¹) and has significant impacts on the performance and efficacy of the electrode material for capacitive performances. This study reveals the energy storage performance of the compositionally engineered S′N-NCS/S-g-CN material in terms of sulfur vacancies, electrochemical kinetics, and the charge storage mechanism.